Image resolution

Last updated

Image resolution is the detail an image holds. The term applies to raster digital images, film images, and other types of images. Higher resolution means more image detail.

Contents

Image resolution can be measured in various ways. Resolution quantifies how close lines can be to each other and still be visibly resolved. Resolution units can be tied to physical sizes (e.g. lines per mm, lines per inch), to the overall size of a picture (lines per picture height, also known simply as lines, TV lines, or TVL), or to angular subtense. Line pairs are often used instead of lines; a line pair comprises a dark line and an adjacent light line. A line is either a dark line or a light line. A resolution of 10 lines per millimeter means 5 dark lines alternating with 5 light lines, or 5 line pairs per millimeter (5 LP/mm). Photographic lens and film resolution are most often quoted in line pairs per millimeter.

Types

The resolution of digital cameras can be described in many different ways.

Pixel count

The term resolution is often considered equivalent to pixel count in digital imaging, though international standards in the digital camera field specify it should instead be called "Number of Total Pixels" in relation to image sensors, and as "Number of Recorded Pixels" for what is fully captured. Hence, CIPA DCG-001 calls for notation such as "Number of Recorded Pixels 1000 × 1500". [1] [2] According to the same standards, the "Number of Effective Pixels" that an image sensor or digital camera has is the count of pixel sensors that contribute to the final image (including pixels not in said image but nevertheless support the image filtering process), as opposed to the number of total pixels, which includes unused or light-shielded pixels around the edges.

An image of N pixels height by M pixels wide can have any resolution less than N lines per picture height, or N TV lines. But when the pixel counts are referred to as "resolution", the convention is to describe the pixel resolution with the set of two positive integer numbers, where the first number is the number of pixel columns (width) and the second is the number of pixel rows (height), for example as 7680 × 6876. Another popular convention is to cite resolution as the total number of pixels in the image, typically given as number of megapixels, which can be calculated by multiplying pixel columns by pixel rows and dividing by one million. Other conventions include describing pixels per length unit or pixels per area unit, such as pixels per inch or per square inch. None of these pixel resolutions are true resolutions[ clarification needed ], but they are widely referred to as such; they serve as upper bounds on image resolution.

Below is an illustration of how the same image might appear at different pixel resolutions, if the pixels were poorly rendered as sharp squares (normally, a smooth image reconstruction from pixels would be preferred, but for illustration of pixels, the sharp squares make the point better).

Resolution illustration.png

An image that is 2048 pixels in width and 1536 pixels in height has a total of 2048×1536 = 3,145,728 pixels or 3.1 megapixels. One could refer to it as 2048 by 1536 or a 3.1-megapixel image. The image would be a very low quality image (72ppi) if printed at about 28.5 inches wide, but a very good quality (300ppi) image if printed at about 7 inches wide.

The number of photodiodes in a color digital camera image sensor is often a multiple of the number of pixels in the image it produces, because information from an array of color image sensors is used to reconstruct the color of a single pixel. The image has to be interpolated or demosaiced to produce all three colors for each output pixel.

Spatial resolution

The terms blurriness and sharpness are used for digital images but other descriptors are used to reference the hardware capturing and displaying the images.

Spatial resolution in radiology refers to the ability of the imaging modality to differentiate two objects. Low spatial resolution techniques will be unable to differentiate between two objects that are relatively close together.

Matakis - blurred.jpg
MARTAKIS1.jpg
Image at left has a higher pixel count than the one to the right, but is still of worse spatial resolution.

The measure of how closely lines can be resolved in an image is called spatial resolution, and it depends on properties of the system creating the image, not just the pixel resolution in pixels per inch (ppi). For practical purposes the clarity of the image is decided by its spatial resolution, not the number of pixels in an image. In effect, spatial resolution refers to the number of independent pixel values per unit length.

The spatial resolution of consumer displays range from 50 to 800 pixel lines per inch. With scanners, optical resolution is sometimes used to distinguish spatial resolution from the number of pixels per inch.

In remote sensing, spatial resolution is typically limited by diffraction, as well as by aberrations, imperfect focus, and atmospheric distortion. The ground sample distance (GSD) of an image, the pixel spacing on the Earth's surface, is typically considerably smaller than the resolvable spot size.

In astronomy, one often measures spatial resolution in data points per arcsecond subtended at the point of observation, because the physical distance between objects in the image depends on their distance away and this varies widely with the object of interest. On the other hand, in electron microscopy, line or fringe resolution refers to the minimum separation detectable between adjacent parallel lines (e.g. between planes of atoms), whereas point resolution instead refers to the minimum separation between adjacent points that can be both detected and interpreted e.g. as adjacent columns of atoms, for instance. The former often helps one detect periodicity in specimens, whereas the latter (although more difficult to achieve) is key to visualizing how individual atoms interact.

In Stereoscopic 3D images, spatial resolution could be defined as the spatial information recorded or captured by two viewpoints of a stereo camera (left and right camera).

Spectral resolution

Pixel encoding limit the information stored in a digital image, and the term color profile is used for digital images but other descriptors are used to reference the hardware capturing and displaying the images.

Spectral resolution is the ability to resolve spectral features and bands into their separate components. Color images distinguish light of different spectra. Multispectral images can resolve even finer differences of spectrum or wavelength by measuring and storing more than the traditional 3 of common RGB color images.

Temporal resolution

Temporal resolution (TR) refers to the precision of a measurement with respect to time.

Movie cameras and high-speed cameras can resolve events at different points in time. The time resolution used for movies is usually 24 to 48 frames per second (frames/s), whereas high-speed cameras may resolve 50 to 300 frames/s, or even more.

The Heisenberg uncertainty principle describes the fundamental limit on the maximum spatial resolution of information about a particle's coordinates imposed by the measurement or existence of information regarding its momentum to any degree of precision.

This fundamental limitation can, in turn, be a factor in the maximum imaging resolution at subatomic scales, as can be encountered using scanning electron microscopes.

Radiometric resolution

Radiometric resolution determines how finely a system can represent or distinguish differences of intensity, and is usually expressed as a number of levels or a number of bits, for example 8 bits or 256 levels that is typical of computer image files. The higher the radiometric resolution, the better subtle differences of intensity or reflectivity can be represented, at least in theory. In practice, the effective radiometric resolution is typically limited by the noise level, rather than by the number of bits of representation.

Resolution in various media

This is a list of traditional, analogue horizontal resolutions for various media. The list only includes popular formats, not rare formats, and all values are approximate, because the actual quality can vary machine-to-machine or tape-to-tape. For ease-of-comparison, all values are for the NTSC system. (For PAL systems, replace 480 with 576.) Analog formats usually had less chroma resolution.

Many cameras and displays offset the color components relative to each other or mix up temporal with spatial resolution:

PPIPixelsmm
800100031.8
300100084.7
2001000127
721000352.8
PPIPixelsmm
8003150100
3001181100
200787100
72283100
PPIPixelsmm Paper size
3009921×14008840×1186A0
3007016×9921594×840A1
3004961×7016420×594A2
3003508×4961297×420A3
3002480×3508210×297A4
3001748×2480148×210A5
3001240×1748105×148A6
300874×124074×105A7
300614×87452×74A8

See also

Related Research Articles

Digital video is an electronic representation of moving visual images (video) in the form of encoded digital data. This is in contrast to analog video, which represents moving visual images in the form of analog signals. Digital video comprises a series of digital images displayed in rapid succession.

Pixel Physical point in a raster image

In digital imaging, a pixel, pel, or picture element is a smallest addressable element in a raster image, or the smallest addressable element in an all points addressable display device; so it is the smallest controllable element of a picture represented on the screen.

Video Electronic moving image

Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode ray tube (CRT) systems which were later replaced by flat panel displays of several types.

DV Magnetic tape-based consumer and broadcast videocassette format for camcorders and video codec

DV refers to a family of codecs and tape formats used for storing digital video, launched in 1995 by a consortium of video camera manufacturers led by Sony and Panasonic. In the late 1990s and early 2000s, DV was strongly associated with the transition from analog to digital desktop video production, and also with several enduring "prosumer" camera designs such as the Sony VX-1000. DV is sometimes referred to as MiniDV, which was the most popular tape format using a DV codec during this time.

Interlaced video Technique for doubling the perceived frame rate of a video display

Interlaced video is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth. The interlaced signal contains two fields of a video frame captured consecutively. This enhances motion perception to the viewer, and reduces flicker by taking advantage of the phi phenomenon.

Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information, taking advantage of the human visual system's lower acuity for color differences than for luminance.

Betamax Consumer-level analog video tape recording and cassette form factor standard

Betamax is a consumer-level analog-recording and cassette format of magnetic tape for video, commonly known as a video cassette recorder. It was developed by Sony and was released in Japan on May 10, 1975, followed by the US in November of the same year.

Digital8 is a consumer digital recording videocassette for camcorders based on the 8 mm video format developed by Sony, and introduced in 1999.

D-1 (Sony) Magnetic tape-based videocassette format

D-1 or 4:2:2 Component Digital is an SMPTE digital recording video standard, introduced in 1986 through efforts by SMPTE engineering committees. It started as a Sony and Bosch - BTS product and was the first major professional digital video format. SMPTE standardized the format within ITU-R 601, also known as Rec. 601, which was derived from SMPTE 125M and EBU 3246-E standards.

Camcorder Video camera with built-in video recorder

A camcorder is an electronic device originally combining a video camera and a videocassette recorder.

The following is a list of video-related topics.

Display resolution Number of distinct pixels in each dimension that can be displayed

The display resolution or display modes of a digital television, computer monitor or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by different factors in cathode ray tube (CRT) displays, flat-panel displays and projection displays using fixed picture-element (pixel) arrays.

High-definition video is video of higher resolution and quality than standard-definition. While there is no standardized meaning for high-definition, generally any video image with considerably more than 480 vertical scan lines or 576 vertical lines (Europe) is considered high-definition. 480 scan lines is generally the minimum even though the majority of systems greatly exceed that. Images of standard resolution captured at rates faster than normal, by a high-speed camera may be considered high-definition in some contexts. Some television series shot on high-definition video are made to look as if they have been shot on film, a technique which is often known as filmizing.

Optical resolution describes the ability of an imaging system to resolve detail in the object that is being imaged.

Low-definition television (LDTV) refers to TV systems that have a lower screen resolution than standard-definition TV systems. The term is usually used in reference to digital TV, in particular when broadcasting at the same resolution as low-definition analog TV systems. Mobile DTV systems usually transmit in low definition, as do all slow-scan TV systems.

Closed-circuit television camera

A closed-circuit television camera can produce images or recordings for surveillance or other private purposes. Cameras can be either video cameras, or digital stills cameras. Walter Bruch was the inventor of the CCTV camera. The main purpose of a CCTV camera is to capture light and convert it into a video signal. Underpinning a CCTV camera is a CCD sensor. The CCD converts light into an electrical signal and then signal processing converts this electrical signal into a video signal that can be recorded or displayed on the screen.

Pixel aspect ratio

Pixel aspect ratio is a mathematical ratio that describes how the width of a pixel in a digital image compares to the height of that pixel.

The Sony DCR-VX1000 was a DV tape camcorder released by Sony in 1995, replaced by the DCR-VX2000 in 2000 and the DCR-VX2100 in mid 2003.

References

  1. Archived 2017-02-02 at the Wayback Machine Guideline for Noting Digital Camera Specifications in Catalogs. "The term 'Resolution' shall not be used for the number of recorded pixels"
  2. ANSI/I3A IT10.7000–2004 Photography – Digital Still Cameras – Guidelines for Reporting Pixel-Related Specifications
  3. http://www.derose.net/steve/resources/video-resolution.html
  4. "Archived copy" (PDF). Archived from the original (PDF) on 2011-09-11. Retrieved 2011-08-31.CS1 maint: archived copy as title (link) Kodak 500t Film spec sheet
  5. An analysis of film resolution
  6. Explanation of MTF
  7. "/Film Interview: IMAX Executives Talk 'The Hunger Games: Catching Fire' and IMAX Misconceptions". Slash Film. December 2, 2013. Retrieved December 17, 2013.
  8. http://www.phaseone.com/en/camera-systems/iq-series.aspx
  9. "Leaf Aptus Medium Format Digital Backs". www.mamiyaleaf.com.
  10. DxO. "Phase One IQ180 Digital Back : Tests and Reviews – DxOMark". www.dxomark.com.
  11. Forret, Peter. "Megapixel calculator – toolstudio". web.forret.com.